福建龙岩大洋花岗岩LA-ICP-MS锆石U-Pb测年、Hf同位素组成及其地质意义

LA-ICP-MS Zircon U-Pb Ages and Hf Isotopic Compositions of Dayang Granite from Longyan,Fujian Province

对福建龙岩大洋花岗岩的两期岩相进行了LA-ICP-MS锆石U-Pb定年和锆石Hf同位素研究。结果表明:大洋花岗岩的早期黑云母正长花岗岩年龄为(144.8±0.9)Ma,εHf(t)值为-5.58～-2.00,二阶段Hf模式年龄为1 313～1 530 Ma,晚期微斜长石花岗岩的年龄为(127.5±0.4)Ma,εHf(t)值为-7.57～-0.90,二阶段Hf模式年龄为1 246～1 668 Ma。同位素特征表明,大洋花岗岩两期岩体都形成于早白垩世,是在岩石圈伸展的底侵作用下形成的,物源主要是中元古代地壳物质,但晚期有少量幔源组分的加入。

A comprehensive research including LA-ICP-MS zircon U-Pb dating and Hf isotopic composition analysis on Dayang granitic pluton was carried out. We obtained the LA-ICP-MS zircon U-Pb ages of （144. 8 ±0. 9） Ma and （ 127.5± 0.4） Ma for the early medium coarse grained biotite granite and the late medium fine grained plagioclase granite in Dayang granitic pluton, respectively. According to zircon Hf isotope analyses, the both εnf（t） values are from -5.58 to -2.00 and from -7.57 to -0.90, and their corresponding Hf two- stage model ages （TDM2） are from 1,313 to 1,530 Ma and from 1,246 to 1,668 Ma, respectively. These data suggest that the magma sources of the two stages in Dayang granite mainly derived from Mesoproterozoic crustal materials, but the second stage involved some portions of mantle component. Dayang granite formed in the Early Cretaceous, which implies that it generated in basaltic underplating under lithosphere extension environment.